Key clinical point: In patients with estrogen receptor-positive/human epidermal growth factor receptor 2-negative breast cancer (ER +/HER2− BC), adjuvant S-1 plus standard endocrine therapy (ET) significantly reduced invasive disease-free survival (IDFS) events compared with ET alone.
Major finding: IDFS events were observed in 16% vs. 11% of patients in ET-only vs. ET+S-1 groups (hazard ratio [HR], 0.63; P = .0003), respectively. The estimated 5-year IDFS was 87% in the ET+S-1 group vs. 82% in the ET-only group. However, adverse events were higher in patients receiving ET+S-1 therapy (99%) vs. ET alone (79%) but were majorly manageable.
Study details: Phase 3 trial included 1,930 women with ER +/HER− BC with intermediate to high risk for recurrence who were randomly allocated to receive either ET alone (n=973) or ET+S-1 (n=957) for a median follow-up of 52.2 months.
Disclosures: This study was sponsored by the Public Health Research Foundation, Japan, and funded by Taiho Pharmaceuticals. Masakazu Toi and other study authors reported funding and ties with various pharmaceutical companies including Taiho during and outside the conduct of the study.
Source: Toi M et al. Lancet Oncol. 2021 Jan 1. doi: 10.1016/S1470-2045(20)30534-9 .